It is well known in the art that cellulose acetate with low degree of substitution have high affinity for water. C. J. Malm (British Patent 356,012 (1929)) disclosed the preparation of cellulose monoacetate by the sulfuric acid-catalyzed hydrolysis of cellulose triacetate in aqueous sulfuric acid. The product, having a DS of 0.6-0.8 acetyls (DS=number of substituents per anhydroglucose ring), was soluble in water. This process included long reaction times, and the necessity for continuous or sequential addition of water to maintain reaction rates, resulting in a dilute reaction mixture and difficulties in recovery of by-product acetic acid. Additionally, the sulfuric acid catalyst promotes rapid degradation of the molecular weight of the polymer.
In U.S. Pat. No. 2,836,590 (1958) H. W. Turner discloses high temperature (&gt;180.degree. C.) alcoholysis of cellulose acetate without the use of catalysts. At the temperatures disclosed by Turner, cleavage of the 1,4-glycosidic linkages of the cellulose ester backbone competes with the desired deacylation.
Russian workers studied the partial hydrolytic elimination of ester groups from cellulose acetate butyrate in acetic acid/water (78% acid) for the purpose of chemically crosslinking these materials with dimethylolethyleneurea. The cellulose acetate butyrate was hydrolyzed to a DS of 1.5 butyryl with no acetyl present. [Vasil'eva, G. G. and Petropavlovskii, G. A., Zhurnal Prikladnoi Khimii, 49, (pp. 622-26 Eng. Trans.) (1976)].
A reference to foaming tendency of benzene solutions of cellulose esters of the higher fatty acids (lauryl, dipalmityl, tripalmityl, and tristearyl cellulose) indicated that the surface tension of these solutions was not responsible for foam formation. [Lee, J. Soc. Chem Ind. Japan 40, Suppl. binding 459 (1937)].
Heretofore, cellulose acetate butyrates and cellulose acetate propionates that have significant surface activity and that form stable foams in aqueous systems have been unknown.